High-fidelity speaker with negative feedback

Abstract

A negative-feedback circuit for use with a moving-coil loudspeaker and a host amplifier modifies the feedback signal from the output of the host amplifier in such a way that the velocity of the voice coil of the speaker more closely follows the signal voltage input to the host amplifier. The power output of the power amplifier is delivered to the voice coil through a low resistance, and a high resistance feedback path is provided from each side of this low resistance to the input of the host amplifier. Other reactive and resistive elements may also be used with the high resistance feedback paths for improved operation.

I claim: 
     
       1. High-fidelity speaker system comprising in combination a moving-coil loudspeaker having a voice coil and a coil input terminal   an audio amplifier associated therewith, said audio amplifier having an input terminal and an output terminal,   an output resistance connected between said output terminal and said coil input terminal, an input resistance,   means for applying an audio voltage signal to said input terminal via said input resistance, whereby a current i, is produced in said input resistance,   an impedance network connecting said input terminal to said output terminal and being so related to said input resistance that the desired amplification is obtained and having components such that there is a point in said network at which the voltage is proportional to di,/dt+i,   and means for causing the voltage at said coil input terminal to track the voltage at said point.   
     
     
       2. System according to claim 1, wherein said tracking means comprises a resistor connected between said point and said coil input terminal. 
     
     
       3. High-fidelity speaker system comprising in combination a moving-coil loudspeaker having a voice coil and a coil input terminal   an audio amplifier of high gain associated therewith, said audio amplifier having a signal input and a power output,   a low resistance connecting said power output to said voice coil,   an impedance network from said power output to said signal input,   said impedance network including a dominating high resistance between said power output and a junction point electrically near said signal input,   and leakage impedance between said junction point and   said coil input terminal.   
     
     
       4. System according to claim 3, wherein said impedance network is part of a model or analog of said loudspeaker, said model being electrically connected between said junction point and said signal input.   
     
     
       5. System according to claim 4, wherein said moving-coil loudspeaker is a multiway loudspeaker system having a crossover frequency and wherein said model or analog includes a first reactive pair parallel-resonant at said crossover frequency and a second reactive pair series-resonant at said crossover frequency electrically connected between said junction point and ground. 
     
     
       6. System according to claim 5 wherein said loudspeaker includes a woofer and wherein said model or analog includes a capacitance in series with the inductance of said first reactive pair and being series-resonant therewith near the mechanical resonant frequency of the mass-compliance combination of said woofer. 
     
     
       7. System according to claim 6 wherein said loudspeaker includes a tweeter and wherein said model or analog includes an inductance in series with the capacitance of said first reactive pair and having a value corresponding to that of the voice coil of said tweeter.